JPH0833133B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for controlling an air-fuel ratio of an internal combustion engine,
In particular, the present invention relates to an apparatus that includes air-fuel ratio sensors on the upstream side and the downstream side of an exhaust purification catalyst and that controls the air-fuel ratio with high accuracy based on the detection values of these two air-fuel ratio sensors.

<Prior Art> As a conventional general air-fuel ratio control device for an internal combustion engine, there is, for example, one disclosed in Japanese Patent Laid-Open No. 60-240840.

Explaining the outline of this, the intake air flow rate Q of the engine
And detects the rotational speed N corresponding to the quantity of air sucked into the cylinder basic fuel supply quantity _{T P (= K · Q /} N; K is a constant) is calculated, and the engine temperature the basic fuel supply quantity T _P Corrected by the air-fuel ratio feedback correction coefficient (air-fuel ratio correction amount) set by the signal from the air-fuel ratio sensor (oxygen sensor) that detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas. Finally, the fuel supply amount T _I
Set.

Then, by outputting a drive pulse signal having a pulse width corresponding to the fuel supply amount T _I set in this way to the fuel injection valve at a predetermined timing, a predetermined amount of fuel is injected and supplied to the engine. .

The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed so as to control the air-fuel ratio near the target air-fuel ratio (theoretical air-fuel ratio). This is interposed in the exhaust system,
The conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that oxidizes CO and HC (hydrocarbons) in the exhaust gas and reduces and purifies NO _X functions effectively in the exhaust state during stoichiometric combustion. This is because it is set to do.

The electromotive force (output voltage) generated by the air-fuel ratio sensor has a characteristic of abruptly changing in the vicinity of the theoretical air-fuel ratio, and the output voltage V ₀ and a reference voltage (slice level) SL corresponding to the theoretical air-fuel ratio SL.
Is compared to determine whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. Then, for example, when the air-fuel ratio is lean (rich), after the feedback correction coefficient α that multiplies the basic fuel supply amount T _P is turned lean (rich), the large proportional constant P is increased (decreased) at the first time, The air-fuel ratio is controlled near the stoichiometric air-fuel ratio by gradually increasing (decreasing) the predetermined integration constant I and correcting the fuel supply amount T _I by increasing (decreasing).

Further, in such an air-fuel ratio control device, the deviation of the air-fuel ratio from the target value in the non-feedback control region or the deviation from the stoichiometric air-fuel ratio during the transient operation in which the operation region during feedback control moves. To control
It is becoming common to perform learning control by setting a learning correction value Kl so that the average value of the air-fuel ratio feedback correction coefficient α approaches a reference value under a predetermined steady-state operating condition during air-fuel ratio feedback control.

By the way, in the normal air-fuel ratio feedback control device as described above, one air-fuel ratio sensor is provided in the collection portion of the exhaust manifolds as close to the combustion chamber as possible in order to improve the responsiveness, but this portion has a high exhaust temperature. Therefore, the characteristics of the air-fuel ratio sensor are likely to change due to thermal influences and deterioration, and it is difficult to detect the average air-fuel ratio of all cylinders due to insufficient mixing of exhaust gas for each cylinder, making it difficult to detect the air-fuel ratio accurately. However, the air-fuel ratio control accuracy was deteriorated.

In view of this point, it has been proposed that an air-fuel ratio sensor is provided on the downstream side of the exhaust purification catalyst and feedback control of the air-fuel ratio is performed by using the detection values of the two air-fuel ratio sensors (Japanese Patent Laid-Open No. 58-48756). See the bulletin).

That is, the air-fuel ratio sensor on the downstream side is difficult to respond because it is far from the combustion chamber, but because it is on the downstream side of the exhaust purification catalyst, the characteristics due to variations in exhaust components (CO, HC, NOx, CO ₂ ) Is less likely to occur, the amount of poisoning due to toxic components in the exhaust is small, and it is less susceptible to characteristic changes due to poisoning, and the mixed state of the exhaust is good, so the average air-fuel ratio of all cylinders can be detected. As compared with the air-fuel ratio sensor, highly accurate and stable detection performance can be obtained.

Therefore, two air-fuel ratio feedback correction coefficients set by the same calculation as described above based on the detection values of the two air-fuel ratio sensors are combined, or the air-fuel ratio feedback correction coefficient set by the upstream air-fuel ratio sensor Compensation of variations in the output characteristics of the upstream air-fuel ratio sensor by correcting the control constants (proportional and integral), the comparison voltage of the output voltage of the upstream air-fuel ratio sensor, and the delay time, etc. by the downstream air-fuel ratio sensor By doing so, highly accurate air-fuel ratio feedback control is performed.

Also in this case, the learning of the above-mentioned air-fuel ratio feedback correction coefficient is also executed in an air-fuel ratio control device equipped with two air-fuel ratio sensors, for example, in Japanese Patent Laid-Open No. 62-62.
-60965, etc.

<Problems to be Solved by the Invention> By the way, as described above, in a case where two air-fuel ratio sensors are provided and an air-fuel ratio feedback correction coefficient as an air-fuel ratio correction amount is learned, the air-fuel ratio sensor on the downstream side is used. Since the fuel ratio correction is a correction for variations in the output characteristics of the upstream side air-fuel ratio sensor, the effects of deviations in the air-fuel ratio caused by factors other than variations in the upstream side air-fuel ratio sensor due to learning are eliminated, and the upstream side air-fuel ratio It is necessary to correct the deviation of the air-fuel ratio that is caused only by the variation of the fuel ratio sensor.

However, in the conventional one, since the correction was made based on the downstream air-fuel ratio detection value while the learning was not in progress, the correction was made including factors other than the variation of the upstream side air-fuel ratio sensor. On the contrary, the air-fuel ratio correction sometimes deteriorates the exhaust emission characteristics.

In particular, the gas detected by the downstream side air-fuel ratio sensor has a long reversal cycle (the update value per time is small) because the air-fuel ratio fluctuation is blunted by the catalyst. Since it takes a very long time to return to the correction amount of, the influence on the exhaust emission and the like becomes great due to the deviation of the air-fuel ratio during that time.

Further, if learning is performed in such a state where the erroneous correction is performed, there is a delay until the learning value converges to a normal value, and there is also a delay in improving the air-fuel ratio performance during the transition due to learning.

The present invention has been made in view of such conventional problems, and in an air-fuel ratio control device for an internal combustion engine equipped with air-fuel ratio sensors upstream and downstream of an exhaust purification catalyst, an air-fuel ratio according to the degree of progress of learning. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which solves the above problems by performing correction.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, the present invention is provided on the upstream side and the downstream side of the exhaust purification catalyst provided in the exhaust passage of the engine, and the exhaust gas changes depending on the air-fuel ratio. First and second air-fuel ratio sensors whose output values change in response to the concentration ratio of the medium specific gas component, and a first air-fuel ratio correction amount is calculated according to the output values of the first air-fuel ratio sensor. First air-fuel ratio correction amount calculation means, second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount according to the output value of the second air-fuel ratio sensor, and the first air-fuel ratio correction amount calculation means Air-fuel ratio correction amount calculation means for calculating a final air-fuel ratio correction amount based on the fuel ratio correction amount and the second air-fuel ratio correction amount, and a learning correction value for storing a learning correction value of the air-fuel ratio correction amount for each operating region. Storage means, the learning correction value retrieved from the learning correction value storage means, and the final correction value. A new learning correction value is set so that the average value of the air-fuel ratio correction amount converges to a predetermined value based on the effective air-fuel ratio correction amount, and the learning correction value corresponds to the learning correction value storage means. In an air-fuel ratio control apparatus for an internal combustion engine, comprising: a learning correction value updating means for updating a learning correction value in an operating region; and a learning progress for making the air-fuel ratio correction amount approach a predetermined value by the learning correction value updating means. And a second air-fuel ratio correction amount that prohibits calculation of the second air-fuel ratio correction amount by the second air-fuel ratio correction amount calculation device until the learning progress degree exceeds a predetermined value. And a calculation prohibiting means.

<Operation> The first air-fuel ratio correction amount calculation means sets the first air-fuel ratio correction amount based on the detection value from the first air-fuel ratio sensor, and the second air-fuel ratio correction amount calculation means The second air-fuel ratio correction amount is set on the basis of the detection value from the second air-fuel ratio sensor after the learning progress determination means has made the learning progress above a predetermined level.

Then, the air-fuel ratio correction amount calculation means calculates a final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount.

On the other hand, the learning correction value updating means stores the learning correction value of the air-fuel ratio correction amount for each operating region from the learning correction value storage means.
A learning correction value for a corresponding operating region is searched for, and a new learning correction value is set so that the average value of the air-fuel ratio correction amount converges to a predetermined value based on the learning correction value and the final air-fuel ratio correction amount. And the learning correction value of the corresponding operating region of the learning correction value storage means is updated with the learning correction value.

However, until the degree of progress of the learning determined by the learning determination means becomes equal to or higher than a predetermined value, the second air-fuel ratio correction amount calculation inhibiting means causes the second air-fuel ratio correction amount calculation means to perform the second operation.
The calculation of the air-fuel ratio correction amount is prohibited.

<Example> Below, the Example of this invention is described based on drawing.

2, an air flow meter for detecting an intake air flow rate Q is provided in an intake passage 12 of an engine 11.
A throttle valve 14 for controlling the intake air flow rate Q in cooperation with the accelerator pedal 13 and the accelerator pedal is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is opened and driven by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects fuel which is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting the cooling water temperature Tw in the cooling jacket of the engine 11 is provided. On the other hand, in the exhaust passage 18, the air-fuel ratio of the intake air-fuel mixture is detected by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion.
An air-fuel ratio sensor 19 is provided, and a three-way catalyst 20 as an exhaust purification catalyst that purifies the exhaust pipe by oxidizing CO and HC and reducing NO _X in the exhaust is provided in the exhaust pipe on the downstream side of the exhaust pipe. Original catalyst
The second side which has the same function as the first air-fuel ratio sensor on the downstream side of 20
The air-fuel ratio sensor 21 is provided.

In addition, the distributor not shown in FIG.
The crank angle sensor 22 is built-in, and the crank unit angle signal output from the crank angle sensor 22 in synchronization with the engine rotation is counted for a certain period of time, or the cycle of the crank reference angle signal is measured to determine the engine rotation. Detect the number N.

Next, the air-fuel ratio control routine by the control unit 16 will be described with reference to the flowcharts of FIGS. 3 and 4. FIG. 3 shows a fuel injection amount setting routine, and this routine is performed every predetermined period (for example, 10 ms).

In step (denoted as S in the figure) 1, the intake air amount per unit rotation is calculated based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on the signal from the crank angle sensor 22. The basic fuel injection amount T _P corresponding to is calculated by the following equation. This step 1
The function of corresponds to the basic fuel supply amount setting means.

T _P = K × Q / N (K is a constant) In step 2, various correction coefficients COEF are set based on the cooling water temperature Tw detected by the water temperature sensor 17.

In step 3, the air-fuel ratio feedback correction coefficient α set by the air-fuel ratio feedback correction coefficient setting routine described later and the learning correction coefficient Kl described later of the air-fuel ratio feedback correction coefficient α are set to the engine speed N and the basic fuel injection amount T _P. Based on and, search and read from the corresponding operation area of RAM.

In step 4, the voltage correction amount T _S is set based on the battery voltage value. This is for correcting a change in the injection flow rate of the fuel injection valve 15 due to the battery voltage fluctuation.

In step 5, the final fuel injection amount (fuel supply amount)
Calculate T _I according to the following equation: The function of step 5 corresponds to the fuel supply amount setting means.

T _I = T _P × COEF × α × Kl + T _{S In} step 6, the calculated fuel injection valve T _I is set in the output register.

As a result, at a predetermined fuel injection timing synchronized with engine rotation, a drive pulse signal having a calculated pulse width of the fuel injection amount T _I is given to the fuel injection valve 15 to perform fuel injection.

Next, the air-fuel ratio feedback correction coefficient setting routine will be described with reference to FIG. This routine is executed in synchronization with the engine rotation.

In step 10, it is determined whether or not the operating conditions are such that feedback control of the air-fuel ratio is performed. When the operating conditions are not satisfied, this routine is ended. in this case,
The feedback correction coefficient α is clamped to the value at the end of the previous feedback control or a constant reference value, and the feedback control is stopped.

In step 11, the signal voltage V _O2 from the first air-fuel ratio sensor 19 and the signal voltage V ′ _O2 from the second air-fuel ratio sensor 21.
Enter

In step 12, the signal voltage V _{O2 of} the first air-fuel ratio sensor 19 input in step 10 is compared with the reference value SL corresponding to the target air-fuel ratio (theoretical air-fuel ratio).

Then, when V _O2 > SL, that is, when it is determined to be rich, the process further proceeds to step 13, and it is determined whether or not immediately after lean → rich inversion.

When reversing, the routine proceeds to step 14, where the current value α ₀ of the air-fuel ratio feedback correction coefficient α and the previous first air-fuel ratio sensor 1
The average value α _M of 9 and the value α ₋₁ when the output is inverted (the value before the proportional portion P _{L is applied} ) is calculated.

In step 15, the absolute value of the deviation Δα between the average value α _M and the predetermined value α _C is compared with the positive reference value Δα ₀ . here,
The predetermined value α _C is a value at which the air-fuel ratio feedback correction coefficient α converges when learning of the air-fuel ratio feedback correction coefficient α described later progresses sufficiently, in other words, the air-fuel ratio feedback correction coefficient α is set to this value α _{C. The} target air-fuel ratio (theoretical air-fuel ratio) is set to a value that can be obtained when clamped to _C.

When | Δα | ≦ Δα ₀ and it is determined that the learning has progressed sufficiently, the routine proceeds to step 16, where the signal voltage V ′ _O2 from the second air-fuel ratio sensor 21 and the target air-fuel ratio (theoretical air-fuel ratio ) Compare with the corresponding reference value SL.

When it is determined that the air-fuel ratio is rich ( _V'O2 > SL), the _routine proceeds to step 17, where the second air-fuel ratio correction amount PHOS for correcting the proportional portion P given at the time of reversal for setting the air-fuel ratio feedback correction coefficient α is set. From the current value PHOS _-1 by a predetermined amount Δ
After updating by the value obtained by subtracting DPHOS, the routine proceeds to step 18, and after updating the second air-fuel ratio correction amount PHOS from the reference value P _R0 of the proportional portion P _R by a value, the routine proceeds to step 21.

When it is determined that the air-fuel ratio is lean ( _V'O2 <SL), the routine proceeds to step 19, where the second air-fuel ratio correction amount PHOS is updated to a value obtained by adding a predetermined amount ΔDPHOS to the current value PHOS _-1, and then step 20. to proceeds, then, the process proceeds updated with increased value of the second air-fuel ratio correction amount PHOS the reference value P _L0 of proportional portion P _L to step 21.

On the other hand, when | Δα |> Δα ₀ is satisfied in step 15, the learning of the air-fuel ratio feedback correction coefficient α has not yet progressed sufficiently, so that the proportional amount P _R is corrected by the second air-fuel ratio correction amount PHOS. Without performing step 21, proceed to step 21.

In step 21, the air-fuel ratio feedback correction coefficient α is updated with a value obtained by subtracting the proportional P _R from the current value.

In this way, after setting the air-fuel ratio feedback correction coefficient α, the routine proceeds to step 22, and the learning correction coefficient Kl of the air-fuel ratio feedback correction coefficient α is set and updated as follows. First, from the engine speed N and the basic fuel injection amount T _P , R
The learning correction coefficient (learning correction value of the air-fuel ratio correction amount) Kl stored in the map of AM is searched, and the deviation Δα is added to the current learning correction coefficient Kl searched according to the following equation by a predetermined ratio. By doing so, a new learning correction coefficient Kl is calculated, and the data of the learning correction coefficient Kl in the same area is corrected and rewritten. That is, the RAM storing the learning correction coefficient Kl corresponds to the learning correction value storage means, and the function of step 22 corresponds to the learning correction value updating means.

Kl ← Kl + Δα / M (M is a constant, M> 1) When it is determined in step 13 that the fuel is rich but not immediately after reversal, the routine proceeds to step 23, where the air-fuel ratio feedback correction coefficient α is integrated from the current value by the integral I Update with the value obtained by subtracting.

On the other hand, when it is determined in step 12 that V _O2 <SL, that is, when lean is determined, the process proceeds to step 24, it is determined whether it is immediately after the rich-to-lean reversal, and when reversing, the process proceeds to step 25, Similar to step 14, average value α _M
Is calculated, and the absolute value of the deviation Δα is compared with a positive reference value Δα ₀ in step 26.

Similarly, when | Δα | ≦ Δα ₀ is determined and it is determined that the learning has progressed sufficiently, the routine proceeds to step 27, where the second
Of the air-fuel ratio by comparing the signal voltage voltage V _'O2 sensor 21 and the reference value SL, after the rich determination time is updated in value the second air-fuel ratio correction amount PHOS by subtracting a predetermined amount ΔDPHOS proceeds to step 28,
The routine proceeds to step 29, where the proportional amount P _R is updated with a value obtained by reducing the second air-fuel ratio correction amount PHOS from the reference value P _R0, and at the time of lean determination, it proceeds to step 30 and the second air-fuel ratio correction amount PHOS is set. After updating the value by adding the fixed amount ΔDPHOS, the process proceeds to step 31, and the proportional amount P _L is set to the reference value P _L0 to the second air-fuel ratio correction amount PHOS.
Is updated with the increased value, and the process proceeds to step 32.

In step 32, the air-fuel ratio feedback correction coefficient α is updated with a value obtained by increasing the proportional amount P _L to the current value, and then the process proceeds to step 22 to update and set the learning correction coefficient Kl.

If it is determined in step 24 that it is not immediately after reversal, the routine proceeds to step 33, where the air-fuel ratio feedback correction coefficient α is updated with a value obtained by increasing the integral I by the current value.

With such a configuration, if the proportional components P _R and P _L are corrected by the second air-fuel ratio correction amount PHOS while the learning of the air-fuel ratio feedback correction coefficient α has not progressed sufficiently, the upstream first Since the correction is performed for factors other than the characteristic variation of the air-fuel ratio sensor 19, the incorrect air-fuel ratio correction is performed and the air-fuel ratio shifts.However, the correction is prohibited during this period, so the The deviation of the fuel ratio can be prevented, and good air-fuel ratio feedback control can be maintained.

In this embodiment, the air-fuel ratio feedback control based on the detection value of the first air-fuel ratio sensor 19 is used as the basis, and the proportional portion of the air-fuel ratio feedback correction coefficient is corrected based on the detection value of the second air-fuel ratio sensor. However, the air-fuel ratio feedback correction coefficient is set by each air-fuel ratio sensor, and the air-fuel ratio feedback correction coefficient obtained by synthesizing both values is used. The present invention can also be applied to the one in which the reference value SL for rich / lean determination and the output delay time are corrected by the detection of the second air-fuel ratio sensor while performing the air-fuel ratio feedback control by the first air-fuel ratio sensor.

The second air-fuel ratio correction amount PHOS is also stored for each operating region divided by the engine speed N, the basic fuel injection amount T _P, etc. (since the reversal cycle is long, the air-fuel ratio feedback correction coefficient α is stored. A learning function may be provided to update the stored value as an initial value when the area changes (roughly divided from the area). Furthermore, the second air-fuel ratio correction amount PHOS is not kept as it is, but an average value of the correction amount PHOS at the time of the inversion and the correction amount PHOS at the time of the previous inversion is calculated for each inversion of the second air-fuel ratio sensor, and The learning correction value may be set by newly weighted averaging the average value and the weighted average value of the past average values. In the case where the learning of the second air-fuel ratio correction amount is performed, the learning of the second air-fuel ratio correction amount naturally stops while the learning of the air-fuel ratio feedback correction coefficient α does not proceed.

The calculation of PHOS in steps 17, 19, 28 and 30 is the second
It corresponds to the air-fuel ratio correction amount calculation means of step 18, 20, 29, 3
The function of calculating the air-fuel ratio feedback correction coefficient α in steps 21, 23, 32 and 33 except for the proportional correction in step 1 corresponds to the first air-fuel ratio correction amount calculation means, and the function of comparison in steps 15 and 26 is It corresponds to a learning means determining means.

The determination of the degree of progress of learning is not limited to the method of this embodiment, and may be a method of determining based on, for example, the number of times of learning or the number of areas in which learning is performed.

<Effects of the Invention> As described above, according to the present invention, the air-fuel ratio sensors are provided on the upstream side and the downstream side of the exhaust purification catalyst, and the air-fuel ratio feedback control is performed based on the detection values of these air-fuel ratio sensors. In the above, since the calculation of the second air-fuel ratio correction amount is prohibited while the learning of the air-fuel ratio correction amount does not proceed sufficiently, the deviation of the air-fuel ratio due to erroneous correction can be prevented, and after the learning is sufficiently advanced, the second By performing the correction based on the air-fuel ratio correction amount, it is possible to execute the air-fuel ratio control with the highest possible accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a flowchart showing a fuel injection amount setting routine of the same embodiment, and FIG. It is a flowchart which similarly shows an air-fuel ratio feedback correction coefficient setting routine. 11 …… internal combustion engine, 12 …… intake passage, 15 …… fuel injection valve,
16 …… control unit, 18 …… exhaust passage, 19 ……
First air-fuel ratio sensor, 20 ... Three-way catalyst, 21 ... Second air-fuel ratio sensor

Claims (1)

[Claims] 1. An output value which is provided upstream and downstream of an exhaust purification catalyst provided in an exhaust passage of an engine and whose output value changes in response to a concentration ratio of a specific gas component in exhaust gas that changes according to an air-fuel ratio. First and second air-fuel ratio sensors, first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to the output value of the first air-fuel ratio sensor, and the second air-fuel ratio Second air-fuel ratio correction amount calculating means for calculating a second air-fuel ratio correction amount according to the output value of the sensor, and a final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount. An air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount, a learning correction value storage means for storing a learning correction value of the air-fuel ratio correction amount for each operation region, and a learning correction value retrieved from the learning correction value storage means. The average value of the air-fuel ratio correction amount is calculated based on the final air-fuel ratio correction amount. A learning correction value updating means for setting a new learning correction value so that the learning correction value converges to a constant value, and for updating the learning correction value in the corresponding operating region of the learning correction value storage means with the learning correction value; In an air-fuel ratio control device of an engine, a learning progress determination unit that determines a progress of learning for bringing the air-fuel ratio correction amount closer to a predetermined value by the learning correction value updating unit, and until the learning progress becomes a predetermined value or more. And an air-fuel ratio correction amount calculation prohibiting means for prohibiting the second air-fuel ratio correction amount calculation means from calculating the second air-fuel ratio correction amount. Control device.